In the early editions, wizards had 9 spell levels and clerics had 7. In 3E, all full caster classes had 9. In 4E, there were potentially as many spell levels as there were levels in the game.
Setting aside the question of whether there should be 0-level "cantrips," how should spell levels work in 5E?
Setting aside the question of whether there should be 0-level "cantrips," how should spell levels work in 5E?